Comment by keeda

Motors with permanent magnets are preferred because they are much more cost- and energy-efficient, even with the painful reliance on REEs. There is a very strong incentive to find alternatives but nothing comparable has been found yet.

There are of course non-electric alternatives like hyrdaulic and pneumatic actuators but they are mostly good for power, not dexterity. The size and complicated fluid dynamics simply are not conducive for fine motor control. I do think these will play a large part eventually because even electric motors cannot economically produce enough force to be practically useful. Like, last I checked, the base-level Unitree robots can lift 2kg or so? Not even enough to lift a load of laundry.

At this point I suspect we'll end up with hydraulics for strength (arms, legs, torso) and electrics for dexterity (grippers)